High Voltage processes have been widely used for power management integrated circuits (PMIC) and switch-mode power supplies (SMPS), both of which are commonly used as LED drivers.
In recent years, interest in efficient “green” electronic devices has steadily increased, driving device manufacturers to seek higher conversion efficiencies and lower standby power consumption. Switch mode power ICs require an integrated start-up circuit and pulse width modulation (PWM) circuit. Unfortunately, conventional high voltage start-up circuits use a power resistor approach wherein power is continuously being dissipated by the power resistor after start-up. The power resistor is selected such that it will provide the charging current for the capacitor and the PWM circuit during start-up operation. The PWM circuit will continue to operate until its Vcc voltage falls below the minimum operating voltage rating, at which point an auxiliary voltage is applied to the Vcc of the PWM circuit. The PWM circuit is normal operation between 5V˜30V.
A further development in recent year is the use of power line voltage (i.e., AC100˜240V) in LED driver ICs to drive LED. These LED driver ICs conventionally use buck converters and include high voltage switch type NMOS to provide current to drive the LED. Conventional solutions also use high voltage depletion MOS to provide reference voltage or power to supply the internal circuit. However, high voltage depletion MOS require extra circuit area and an extra mask to form. Thus, there is a need for an alternative to existing conventional solutions.